Various ambulatory medical devices are known for treating and/or monitoring patients at a remote site away from the caregiver's or clinician's office. One example of an ambulatory medical device is a drug delivery device, such as a drug pump, for providing periodic or continuous drug delivery to the patient when the patient is away from the caregiver's office. Ambulatory drug pumps are shown for example in U.S. Pat. Nos. 4,559,038, 5,531,697 and 5,695,473, the disclosures of which are incorporated by reference.
Certain drugs rarely achieve their maximum therapeutic action through conventional injection techniques. Many drugs reach their full potential only through precise delivery over an extended period of time. With controlled drug infusion through a drug pump, the drug can be given at a precise rate that will keep the drug concentration within the therapeutic margin and out of the toxic range. Ambulatory drug pumps can provide appropriate drug delivery to the patient at a controllable rate which does not require frequent medical attention and which allows the patient to leave the hospital or caregiver's office.
Ambulatory drug pumps typically provide the patient with a drug or agent in liquid form, administering the liquid to the patient through a flexible conduit. Some drugs are sold in a powdered form. Examples of drugs on the market today that are sold in powder form include ampicillin, vancomycin hydrochloride, penicillin, nafcillin, and Desferal.TM. deferoxamine mesylate. Before powdered drugs are administered, they must be mixed with a liquid agent. When powdered drugs are dispensed at pharmacies, the pharmacist typically adds a liquid agent, such as a diluent, to the powdered drug at the pharmacy and then gives the drug to the patient in a liquid form, for example, in a drug pump cassette. The patient could then use the liquid drug with an ambulatory drug pump. Examples of liquid agents that may be mixed with powdered drugs are sterile water, dextrose and saline. These mixing steps require significant pharmacist time and may cause a long wait for a patient who is filling the prescription. Current ambulatory drug pump cassettes do not conveniently allow the patient to perform the dilution or reconstitution of a powdered drug, so the patient must visit the pharmacist.
Certain types of drugs, such as ampicillin, have limited stability in liquid form. These drugs must be mixed with a liquid agent only a short period of time before they are administered to the patient. The short-lived stability of these drugs necessitates frequent trips by the patient to pick up the diluted drug or frequent deliveries of the diluted drug to the patient's location. In the alternative, some patients are taught to mix drugs with a liquid agent at home. If known drug cassette configurations are used, this process may be awkward and cumbersome for the patient.
Another problem with filling cassettes for ambulatory drug pumps is the elimination of air from the reservoir within the cassette. Typically, cassettes are filled by injecting fluid through a delivery conduit that is connected to the cassette reservoir. The delivery conduit is a tube that connects the cassette to the patient for drug delivery. Pharmacists will typically use a syringe or a pump to move the drug to be administered into the cassette reservoir. After the cassettes are filled, however, trapped air may be present in the cassette reservoir. Typically, the pharmacist will manually remove the trapped air from the cassette reservoir.
In one technique for manually removing trapped air, the cassette is tapped until all the air bubbles have collected, and can be drawn out with a syringe. This process is repeated until all of the air bubbles have been removed. The method is time-consuming and labor-intensive for the pharmacist.
There is a need for drug delivery systems and methods which address the above-mentioned concerns, concerns about drugs that require dilution and/or reconstitution before administration, and concerns about trapped air in the cassette reservoir.